When I first arrived in California many years ago, it was difficult to find good topographical maps. Sure, you could buy maps of Yosemite or Sequoia National Parks (at 1:62,000 scale or somesuch), but if you wanted to buy a map of a random place where you thought it would be fun to hike, you were mostly out of luck. The local REI might have had some maps, but without complications or preordering, it wasn’t easy.
Now, instead, it is maps nirvana. You can have free topo maps of most places in the US on your Mac / PC! Here is how.
Head over to Garmin, and download their excellent Garmin Basecamp software. Install also Garmin MapInstall and MapManager (here is a link for the Mac version). Then, head over to GPS File Depot, and download free maps. The ones I prefer are those by John_M; for the Western US in particular I recommend this one.
You can install the maps on your Mac (or Windows box, I guess), and use them from Garmin Basecamp. It is simply wonderful. Of course, Google Earth is also very good to explore places, but I find the ability to view and print topo maps invaluable for hiking. And perhaps it’s just me, but I still get more information out of a good topo map than out of Google Earth, when it comes to hiking.